The inorganic/polymer composite nanomaterials, which refer to the composite materials, are produced by compounding inorganic nanoparticles with organic high polymers (e.g., plastics, rubbers, etc.) as the continuous phase. The inorganic/polymer composite nanomaterials not only have the advantages of rigidity, dimensional stability and thermal stability of inorganic nanoparticles, but also have the advantages of processability, toughness and dielectric properties of polymers. They can achieve the superiority not possessed by an individual component through synergy among the components and it can prepare a new high polymer composite material, which has broad application foreground in mechanics, optics, electronics, magnetics, biology and other fields. In practical applications, however, since the inorganic nanoparticles are easy to glomerate in a polymer matrix and difficult to disperse, and have poor compatibility with polymers, there is often no real orderly assembly between the inorganic nanoparticles and the polymers. Uniform dispersion of nanoparticles is the foundation of nanostructure, and also an important properties of composite materials. The inorganic nanoparticles are poor in dispersibility and difficult to be interfused, and are easy to produce an inorganic phase aggregate in the composite material, thus they are neither able to be compounded with polymers on a nano scale nor able to better play nanometer effects, limiting their wide application. In addition,the high cost of inorganic nanoparticles is also the reason of their applied limitation.
Therefore, if the inorganic nanoparticles are first subject to surface chemical modification with organic compounds that are both inexpensive and environmentally friendly, so as to improve their dispersivity and surface polarity to produce inorganic/organic composite nanoparticles, and then the composite nanoparticles are compounded with polymers to produce the composite nanomaterial, the glomeration among the inorganic nanoparticles can be effectively prevented, which will improve their compatibility with the polymers and their application properties.
Currently, the surface chemical modifiers of the inorganic nanoparticles are mainly fatty alcohols, amines, fatty acids, silicones, etc., most of which come from fossil resources. While lignin, the biomass resource preceded only by cellulose in content in nature, is rarelyapplied in this field.
Non-renewable fossil resources are increasingly depleted, and environmental issues of papermaking waste are becoming increasingly prominent, making recovery and utilization of the lignin renewable resource in the papermaking waste particularly important. lignin is the only non-petroleum resource in nature that can provide renewable aryl compounds, accounting for about 20%-30% by weight of the plant body. In the pulping and papermaking process, the lignin within the plant body is usually dissolved out to become a main component of the waste liquid, and therefore recovery and utilization of the industrial lignin is an effective way to manage the pulping and papermaking waste liquid issues. With currently more than 30 million tons of industrial lignin produced annually all over the world, using abundant and inexpensive alkaline lignin as the raw material to develop new products and open up new fields of application will help promote the “clean production and recycling economy” of the pulping and papermaking industry, which is in line with sustainable development objectives and has positive environmental and social significance.
The alkaline lignin moleculesextracted from the papermaking waste liquid, containing phenolic hydroxyl group, carbonyl group, benzene ring, ether bond, carbon-carbon double bond, etc., rich in active hydroxyl groups on the surface, can be endowed with excellent reactivity and adsorption properties through chemical modification, achieve the hydrophilic-lipophilic balance value of different proportions, and therefore be stably dispersed in polymers of different polarity. Besides, lignin is renewable, degradable, nonpoisonous, inexpensive and widely available and has other advantages and is an excellent “green” chemical raw material, and therefore its comprehensive utilization draws much attention.
The modified alkaline lignin has been widely used as a dispersant in pesticides, ceramics, coal water slurry, cement, dyes and other fields. However, with development and utilization of the alkaline lignin currently still at a low value-added level, how to utilize the widely available industrial lignin to develop a greater variety of lignin products with excellent properties to achieve the high-value utilization of lignin will become an important direction of the lignin research. Efficiently modifying the alkaline lignin to prepare the lignin type nanomaterials will bring novel and wide application foreground for lignin, and also promote the high-value utilization of lignin to a new height.
A Chinese patent CN 101173107B disclosed lignin-inorganic nanocomposite materials and preparation method therefor on Mar. 16, 2011, which used the following preparation method: First pretreating the inorganic nanoparticles with lignosulfonic acid, ammonium lignosulfonate and other water-soluble lignin surface treatment agents and coupling agents, then adding them to the lignin or their derivatives, and then carrying out acid precipitation, filtration and drying to obtain the product. Cheng Xiansu et al. (Chen Yunping, Cheng Xiansu, Preparation of lignin-based composite materials and their application in ethylene-propylene rubber [J] 2009, 29 (2): 36-40) prepared an ethylene-propylene rubber reinforcing agent by compounding high boiling solvent lignin and nano silica, with the preparation method similar to the aforementioned patent (CN 101173107 B). Hawari J. et al. [Saad R., Hawari J. Grafting of lignin onto nanostructured silica sba-15: preparation and characterization [J]. Journal of Porous Materials, 2013, 20 (1): 227-233] used triethoxy chlorosilane to react with lignin, then blended with the nano silica prepared by the sol-gel method, and then refluxed in toluene before flushing with pyridine, and finally dried to obtain the composite particles.
Currently, preparation of the lignin/inorganic nanocomposite particles has many disadvantages: (1) In the preparation process, expensive silane coupling agent, titanate coupling agent, zirconate coupling agent, etc., or an organic solvent which contain certain toxicity needs to be used as an assistant for surface modification of inorganic nanoparticles, and the preparation cannot be performed at room temperature and atmospheric pressure, thus increasing the cost; (2) the lignin used, undergoing no necessary chemical modification, cannot achieve dispersibility fundamentally; with weak interaction between lignin and inorganic nanoparticles, the inorganic nanoparticles can be pre-dispersed only after a lignin surface treatment agent is additionally added as a dispersant. Therefore, the prepared composite nanoparticles still suffer from serious surface agglomeration, difficult to have their properties improved significantly in application to high polymer materials.